Gasification processes, such as integrated gasification combined cycle (IGCC), used to convert coal and/or petroleum coke to a synthesis gas (syngas), produce a gasifier waste stream containing pollutants. The gasifier waste stream, often referred to as black water, contains high levels of suspended solids, such as slag and fly ash. Thus, the gasifier waste stream must be treated before it can be discharged or reused. A portion of the suspended solids in the gasifier waste stream may be removed in a solids separator or clarification process. This separation process generally requires a large quantity of polymers and flocculants to help promote settling of the suspended solids. After settling at least some of the suspended solids in the gasifier waste stream, the resulting grey water, is directed to one or more evaporators to recover relatively clean water and solids for disposal.
Upsets in the operation of black water solids separators, however, are very common. During these upsets, the gasifier waste stream overflows the solids separator and is directed to the downstream evaporator(s). The high levels of suspended solids in the gasifier waste stream cause fouling in various elements of the evaporator(s). Accordingly, the evaporator(s) need to be taken-off line and mechanically cleaned to remove accumulated slag deposits. This results in delays in treating the gasifier waste stream, which is costly and inconvenient.